The invention relates generally to surge brakes for use in braking trailer vehicles, and more specifically to an improved articulated brake shoe for use in surge brake mechanisms of trailer vehicles.
Surge brake mechanisms are widely used on trailer vehicles to provide a means for braking the forward movement of such vehicles independent of direct control or power from a towing vehicle. Known surge brake systems rely on hydraulic actuators which are operated in response to the forward inertia of the trailer vehicle acting on a decelerating tractor vehicle. Whenever the trailer vehicle is moving relatively toward the tractor vehicle, telescoping members of an actuator unit of a conventional surge brake mechanism will supply pressurized fluid to operate the trailer braking mechanism. The surge brake thus operates to brake a forwardly moving trailer vehicle in response to braking action of its tractor vehicle. Pressurized fluid will also be supplied by the actuator unit, however, if the tractor vehicle is used to back up a trailer vehicle. The surge brake mechanism must, therefore, discriminate between the braking motion of a tractor vehicle wherein the trailer braking action is desired, and backing up of the tractor vehicle wherein a trailer braking action is not desired.
Surge braking mechanisms which effectively discriminate between the two situations are known in the art. One example of such a mechanism is disclosed in U.S. Pat. No. 2,973,839. These mechanisms rely on the fact that the wheel of the trailer vehicle is rotating in a forward direction when the trailer braking operating is desired and is rotating in an opposite or reverse direction when a trailer braking operation is not desired. It has been noticed, however, that a "catch" or abrupt application of the braking mechanism can occur in conventional mechanisms shortly after the transition from a rearward movement of the trailer vehicle to a forward movement thereof. This sudden application of the trailer vehicle brakes is thought to be a result of the relatively large amount of "play" or articulation permitted between the articulated brake shoes of the trailer brake mechanisms and their associated supporting lever arms or plates. During such transitional movement, the articulated brake shoes move from a contact position with the brake drum to a normal towing position free of the brake drum. However, in the transition it appears that the brake shoe overruns its normal towing position and engages the brake drum of the trailer vehicle resulting in a sudden but temporary application of the trailer brake.
The present invention provides a novel articulated linkage system between the articulated brake shoe ad its supporting lever which acts to limit the amount of "play" between the articulated brake shoe and its supporting lever so as to eliminate the sudden application of the trailer vehicle brakes during the transition from rearward movement to a forward or towing movement of the trailer vehicle.